Most electrical systems are supplied by one kind of energy source, e.g., batteries, wind energy, solar energy, or utility energy. Certain special cases are supplied by two sources, such as uninterruptible power supplies. Electrical systems would beneficially be supplied by energy sources of all kinds. Renewable sources are of particular interest, as resources are further distributed about the terrestrial power grid. In islanded power systems, interfacing of multiple sources allows for improved reliability, flexibility, and use of preferred energy sources. The different sources, such as photovoltaic cells, fuel cells, and batteries, generally have different voltage and current characteristics. In some cases, one source is preferential to others; in other cases, a simultaneous combination of sources is appropriate for energy or resource use. Typically, each different source requires a different power converter. As a result, a single-input power converter may be utilized for converting the energy of a particular power source. However, a system with multiple single-input power converters can become complex with a large number of energy sources. As a result, multiple-input power converters may be used to convert energy from multiple energy sources. By integrating all the energy sources through a single conversion device, the structure is simplified resulting in a low cost, unified control and compact system.
Multiple-input power converters can be divided into the following categories: time-sharing multiple-input power converters, multiple-input power converters with pulsating current source cells; multiple-input power converters with pulsating voltage source cells; multiple-input power converters with alternative pulsating current source cells; multiple-input power converters with alternative pulsating voltage source cells; multiple-winding magnetic coupled multiple-input power converters; and multiple-input direct-connected push-pull power converters. Unfortunately, energy conversion using such multiple-input power converters either involves the utilization of a significant number of components or limited voltage conversion ratios which result in significant switching losses, a reduction in converter efficiency, and a limit in the scope of multiple-input power converter applications.